Dual chamber orifice fittings are often sealed by an isolation valve. The isolation valve allows an orifice plate to be replaced or inspected without the need to depressurize or interrupt the flow through the associated flow lines. One example of an orifice fitting with an isolation valve can be found in U.S. Pat. No. 5,474,103 (Klak) entitled “Safety Guard for Orifice Fitting Device”.